Light fixtures or illumination devices creating various effects are getting more and more popular in the entertainment industry in order to create various light effects in connection with entertainment shows. Other fields of application where illumination devices having the capability of changing color are used, are applications in theatres, shops, private homes, discotheques etc.
Typically, such illumination devices with variable color light comprise a plurality of light sources, such as LEDs emitting light in different source colors, wherein the color of each illumination device is obtained by a combination of the source colors of the different light sources. The light from the different light sources is combined in the illumination device. The color of the illumination device can be varied by varying the intensity of each light source such that the combined spectral distribution of the different light sources within the illumination device varies when the intensities of the light sources are varied. This means that the color emitted by an illumination device can be changed by changing the intensity of the light sources.
Recently, the use of LEDs as light sources in an illumination device became more popular. By way of example, three different LEDs of different colors, e.g. a blue LED, a red LED and a green LED (RGB) may be used to generate different colors. For the illumination of a stage or a building, a large number of different illumination devices are normally used to generate a certain illumination. However, when light from several illumination devices is combined into one illumination, color differences might occur as the light sources used in two different illumination devices might differ. The reason for this is the fact that it is difficult to manufacture light sources emitting the exact same color and brightness.
One possibility to overcome the problem when different illumination devices are combined could be to store the spectrum of each light source and to use the spectrum of each light source to calculate the resulting color when the intensities of the light sources are varied. It can be calculated how the intensity of the different light sources should be varied in order to generate a certain target color. However, this system requires knowledge of the spectral distribution of the light sources in order to be able to perform the calculations. This requires that these spectral distributions are measured, particularly because many light fixture vendors do not specify the spectral distribution. Such a system, is known from WO 01/36864 A2.
The colors achievable by an illumination device are called the individual or actual color gamut. This color gamut can be seen as an area within a color map such as CIE 1931 color diagram and the area is defined by the color coordinate points, one for the resulting color of the individually controllable strings. It is to be understood that term light source do also include a collection of a plurality of light sources controlled by the same control signal, such that the coordinate points are obtained as a combination of all the light sources in the collection. E.g. in a typical LED device each of the primary light sources Red, Blue and Green are embodies as respectively a string of red, green and blue LED. By way of example, when three different light sources such as red, green and blue or other light sources emitting cyan, magenta and yellow are used, each light source defines a point in the color space. By way of example, when three different light sources are used, a triangle is generated by the three different light sources by combining the different points in the color space. Each illumination device has its own actual color gamut. When the color gamuts of different light fixtures are combined, a common color gamut is obtained, this common color gamut containing all colors that all the fixtures of a color control system can process simultaneously based on the light sources used by the different light fixtures. This common gamut can be a predefined gamut, e.g. defined by the manufacturer of the different light sources.
EP 1 938 666 B1 discloses a color control using the color gamut of the individual color system of each fixture.
As mentioned above, it is possible to generate each color within the common color gamut by all of the illumination devices. A color can be inter alia defined by the parameters hue and saturation. In the CIE 1931 diagram, the saturation can be seen as the distance from the centre of the color diagram corresponding to the white color to the border of the gamut. This means that the colors with 100% saturation are placed on the outer curve of the CIE diagram and the outer curve of the each individual gamut defines the maximum saturation that the illumination device can generate. As the common gamut is normally smaller than each individual gamut, the situation may occur that the obtained color generated by each of the light fixtures has a color saturation that is not satisfying when the generated colors are limited to the common gamut. Some of the light fixtures may be able to generate colors with more saturation, whereas other light fixtures are not able to generate the color with the same saturation. Thus, with current color control systems it is possible to obtain the same color from all light fixtures of a system, when colors are selected that are located within the common color gamut. This helps to obtain a uniform color output by the system; however, the saturation of the obtained colors may be poor. In other systems where the common color gamut is not taken into account, the user may obtain more saturated colors; however, the user cannot obtain uniform colors.
Thus, in view of the above-said a need exists to provide more flexibility to the user as far as color conformity or color saturation are concerned.